The invention relates to apparatus for filtering solid particulate matter from fluids and, in particular, to improved filters formed from thin, porous walled honeycomb structures and means for mounting the filters for advantageous operation.
The removal of solid particulate matter from fluids (gases or liquids) in which they are mixed is typically accomplished by means of filters made from solid materials formed into articles or masses and having a plurality of pores extending through them (which may be interconnected) of a small cross-sectional size such that the solid materials are both permeable to the fluids and capable of restraining most or all of the solid particulate matter carried by the fluid from passing through the article or mass. Such pores constitute what is termed "open porosity" or "accessible porosity." The minimum cross-sectional size of some or all of the pores can be larger than the size of some or all of the particulates to be filtered, but only to the extent that all or significant desired amounts of sufficiently large particulates become trapped on the inlet surfaces and/or within the pores during the transit of the fluid through the article or mass.
A pending application Ser. No. 165,646, filed July 3, 1980, assigned to the assignee of this application, describes honeycomb filters preferably formed from extruded and sintered ceramic materials which may be used for removing carbonaceous particulates from diesel engine exhaust gases and for other high temperature fluid filtering applications. The filters are of honeycomb structure each comprising a matrix of thin, porous interconnected walls which define inlet and outlet end faces on opposing outer surfaces of the filter and a plurality of hollow passages or cells which extend through the filter body between the inlet and outlet end faces. The thin, porous cell walls may form the outer surface of the filter body between the end faces but more typically, a somewhat thicker, smooth continuous surface or skin is provided surrounding the cells for strength, uniform outer dimensioning, etc.. One end of each of the cells is blocked to form inlet and outlet cells, the inlet group of cells being blocked near the outlet end face and the inlet group of cells being blocked near the outlet end face. The opposing end of each of the cells remains open at the opposing end face. The inlet and outlet cells are alternated so as to adjoin one another and share in common the thin porous walls which define each of the cells. A contaminated fluid introduced under pressure to the inlet end face passes into the filter body through the inlet cells and is forced through the thin, porous walls, which trap the solid particulates present in the fluid, and into adjoining outlet cells through which the now cleansed fluid exits the filter body. Particulates are deposited on the thin wall surfaces of the inlet cells or are trapped in the pores within these walls. Various improvements to the described filter bodies, including filtration through the larger dimensions of the thin porous walls shared by adjoining inlet cells and the provision of asymmetric inlet and outlet cell thin wall surface areas are described and claimed in other copending application Ser. Nos. 350,998, 350,995, and 350,994 all filed on Feb. 22, 1982, which are assigned to the assignee hereof and incorporated by reference.
The described honeycomb filters are typically positioned for use in a housing or can which is installed across or as a component of conduits transporting contaminated fluid to and filtered fluid from the filter. A seal is formed along the outer longitudinal surface of the filter and an inner surface of the surrounding conduit structure to channel contaminated fluid to the inlet face and filtered fluid from the outlet face and to prevent the contaminated fluid from bypassing the filter body. Means used to form the seal may also support and fix the position of the filter with respect to the conduit. Typically, means are provided at either end of the filter body or along the longitudinal outer surface extending between its inlet and outlet end faces both to hold the body in position within the supporting conduit structure and to provide the aforesaid seal. For example, a seal may be formed about the diesel engine exhaust gas filter in the manner described in the aforementioned application Ser. No. 165,646 by providing flange-like mounting members or other comparable mounting members protruding from the inner surfaces of the surrounding conduit structure which are compressed against the outer edges of the filter's opposing inlet and outlet end faces. Seals are sometimes also formed by packing a suitably impermeable material into a gap formed between the longitudinal outer surface of the filter and the support structure, either at the ends of the filter, or along a substantial portion of the outer longitudinal surface of the filter, between the filter and the conduit structure so as to provide both the required support and a seal in a single manufacturing step. In each case, the seal thus formed prevents the flow of the fluid along any appreciable length of the outer surface of the filter extending between its inlet and outlet faces. An additional problem is created by the first described sealing method in that pressing flanges, O-rings or the like against the end faces tends to cover and block the cells located at the periphery of the end faces reducing the effective volume of the filter body and, in a filter used with a hot fluid, to create radially oriented thermal gradients giving rise to possibly detrimental thermal stresses within the filter.